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T. A. EDISON. DUPLEX TBLEGIRAPH.

No. 480,567. Patented Aug. 9, 1892.

UNITED STATES PATENT OFFICE.

THOMAS A. EDISON, OF NEWARK, NEW JERSEY, ASSIGNOR, BY MESNE ASSIGNMENTS,TO THE WESTERN UNION TELEGRAPH COMPANY.

DU PLEX TELEGRAPH.

SPECIFICATION formingpart of Letters Patent No. 480,567, dated August 9,1892.

Application filed September 1, 1874. Patented in England February 5,1875, N0. 384 in France April 28. 1875 No. 107,859; in Italy April 30,1875, Nos. 2,940 and 7,803; in Austria-Hungary June 28. 1875, No. 2,936and ITO-14,584, and in Russia May 24, 1878.170. 3,163.

To all whom it may concern.-

Be it known that 1, THOMAS A. EDISON, of Newark, in the county of Essexand State of New Jersey, have invented an Improvement in DuplexTelegraphs, of which the following is a specification, and for which Ihave obtained foreign patents in the following countries; Great'Britain,dated February 5, 1875, No. 384; France, dated April 28, 1875, No.107,859; Italy, dated April 30,1875, Nos. 2,940 and 7,803;Austria-Hungary, dated June 28, 1875, No. 2,936 and No. 14,584, andRussia, dated May 24, 1878, No. 3,163.

The object of this invention is to enable two operators tosimultaneously send over one wire in onedirection, by reversal of abatterycurrent in one instance and increasing and decreasing thestrength of the current in the other instance, and the connections areso arranged that the party at the receiving-station can signal to thesender to repeat in case of inaccuracy. By combining the apparatus andmethod hereinafter described with any suitable known method ofsimultaneous double transmission in opposite directions fourtransmitting-operators and four receiving-operators can worksimultaneously over one wire, two of each being at each end.

In the diagram Figure 1 I have only shown the transmitting apparatus fortwo operators at one end of the line and the receiving apparatus for thetwo operators at the other end of the line. Fig. 2 is a diagramrepresenting a modification of one portion of the circuits.

The battery a b is composed of unequal elements. Suppose a to representseventy-five cells and b twenty-five cells. The single-circui tkey ortransmitter e modifies the strength of the current passing from thebattery to the line by cutting in or out a portion of the entirebattery; but it has no effect upon the polarity. It is a three-point keyof well-known construction, its arrangement being such that the wire 5is alternately connected with the wire 4 or with the wire 6. When thecurrent passes through the wire 4, a portion of the battery only is inaction; but when the current passes through the wire 6 the whole batteryis inaction, and this change is produced by the elevation or depressionof the key 6, which when depressed brings into action the whole batteryand when elevated leaves a portion of it only in action. This key ortransmitter e is preferably operated by means of an electro-magnetd anda local battery, in connection with a finger-key c. The wire 5 isattached to an insulated contact-spring upon the transmitter e, by meansof which, when the circuit is shifted from the wire 4 to the wire 6, orvice versa, by the movement of the transmitter, one circuit is alwaysclosed before the other is broken. Hence when the finger-key c is openthe section b only of the main battery or b is in circuit through wire4, but when the key 0 is closed the Whole battery a b is in circuitthrough the wire 6. This change in the power of the battery affects thecorresponding instrument at the re oeiving-station, as hereinafter setforth.

The double-current or current-reversing key or transmitter f 11 controlsthe polarity of the current passing from the battery to the line,whether the whole or a portion of the battery is in action, andtherefore has no effect upon its strength. It virtually consists of twosingle-current or three-point keys f. and '5, insulated from each otherand mounted upon the same axis, so as to move together. It is preferablyoperated by the electro-magnet g, local circuit, and key h. When the keyh is open as shown, the current from 5 passes by 10, 11, f, 12, and 13,out through tell-tale magnet kto the line 1, and the return is throughground to 14, spring 15, lever-arm z, 16, and 3. When the key f isattracted by g, the circuit connections are reversed, so that thecurrent from 5 passes by 10, 15, and, 14 to ground, thence returning,through line 1, 13, 12, 16, and 3 to battery.

By bearing in mind that one operator at 0 makes his signals by changingthe amount of battery-power, and that without breaking the metalliccircuit, and that the operator at h signals by reversing the circuit,regardless of the battery-power and without breaking the metallicconnections, it will be understood that both parties can work withouthinderance from the other. It now becomes necessary to show whatinstruments at the receivingstation are employed, the one to respond bythe change of battery force, regardless of polarity, and the other torespond by change of polarity only, regardless of battery force.

The polarity relay-magnet m is in the line Z and is made with apermanent or magnetized armature. Hence it will only respond when thecircuit is reversed, and when it does respond by the reversal of thecircuit by the operator of h the armature-lever works a local circuitand sounder n. The electromagnet o is also in the main-line circuit thatpasses by 20 and key 19 to the earth. The normal condition of this key10 is closed; but whenever either of the parties receiving perceives anyinaccuracy or interruption of the message then the parties sending arenotified by either receiver breaking the circuit at the key 1), and thetell-tale magnet 70, no longer responding to the pulsations of the keysh or 0, indicates to the senders that the circuit is broken.

In order to produce a receiving-instrument that is operative only by theexcess of the current, the spring of the armature s is tightened to theproper degree of tension, so that the magnet 0 will not respond exceptwhen the closing of the key 0 brings the entire battery a 12 intoaction.

If a reversal of current takes place when the entire force of battery ison the magneto, there occurs a false movement of the armatu re 3. Toprevent an incorrect record or sound, the local circuit and receivinginstrument are made as next described.

The local circuit and battery u is constantly operative in thereceiving-magnet or sounder t, and hence the armature of if only fliesback when an opposing current is sent through i to neutralize thecurrent of u and demagnetize the core. This is efiected by the battery71 and circuit that is closed by the lever s on the back movement. Hencewhen 8 is attracted by 0, the circuit of '0 being broken allows u to actunbalanced and gives the sound; but should s fly back on reversing thecurrent it will be so instantly reattracted by 0 as to prevent thecircuit 1; being closed long enough to neutralize the action of u. Hencethe signals given by the operator at a will be correctly responded to bythe receiver 25.

The diagram Fig. 2 shows a modification of the receiving-circuit toprevent a false indication at the receiver.

The armature s operates the circuit of the battery 1; to theelectro-magnet o, and the armature of 0' closes and opens the circuit ofa to the receiving-instrument or sounder t, and as the magnet 0' israther sluggish in movement its armature does not have time to move andbreak the circuit '21, before the armature again flies back, should thecircuit connections have been reversed while the key 0 is closed.

I claim as my invention- 1. The method herein described of transmittingtwo distinct messages by separate operators over one wire in the samedirection and at the same time, one being transmitted by reversal of thebattery-current and the other by increasing or decreasing the currentfrom the battery, substantially as described.

2. A receiving instrument or relay 0 in the main-line circuit, incombination with a local relay 0, whose electro-magnet is brought intoaction through the back contact-stop of the main-line relay, and asounder or other instrument whoseelectro-magnet is broughtinto action bymeans of the local relay 0', substantially as and for the purposes setforth.

3. The receiving instrument or sounder tin the constant battery-circuitu u, in combination with the balancing local battery '0, circuit andcircuit-closing armature s, and electro-magnet 0, substantially as setforth.

4. In the duplex telegraph arranged for sending two separate messagessimultaneously in the same direction and from the same end, thecircuit-breaking key 19 at the receiving end and the tell-tale magnet kin the line at the transmitting end, as and for the purposes set forth.

5. In a single-line telegraphic system for the transmission of twoindependent mes sages, the combination at one station, substantially asspecified, of two independent electrically-connected keys, one for eachoperator, one of which keys when operated reverses the polarity of theelectric current independently of the position and action of the secondkey, which second key controls the strength of current, substantially asset forth. Signed by me this 19th day of August, A. D. 1874.

THOS. A. EDISON.

